This invention relates to pipe repair and installation procedures. In particular, this invention relates to a method and device for facilitating the welding of a permanent cap onto a pipe, for example as part of a natural gas pipeline bypass procedure.
Gas company crews are required on a routine basis to install bypasses on existing piping systems. In most cases bypasses are required as a result of pipeline relocations or damages to the pipeline caused by a third party such as a construction crew. While typically such bypasses involve relatively short pipe lengths, bypasses can involve very long pipe lengths, for example half a mile or more. It is costly and inconvenient to de-energize the entire pipeline for such a bypass procedure, and accordingly gas companies employ a xe2x80x9chotxe2x80x9d tapping and plugging process on the live gas pipe in the bypass operation.
In a conventional gas pipe bypass operation, a xe2x80x9cteexe2x80x9d fitting is secured to the live gas pipe and a stopper is lodged into the pipe through the tee fitting immediately adjacent to each end of the section of pipe to be bypassed. For example, the three-way tee fitting sold as xe2x80x9cSHORTSTOPPxe2x80x9d (trademark) manufactured by T. D. Williamson, Inc. is welded to the pipe exterior at each end of the section of pipe to be bypassed, and the bypass pipe is welded to the stem of the tee, as shown in FIG. 1. The SHORTSTOPP fitting is in turn fitted with a tap/stopper assembly, for example the valve fitting sold as xe2x80x9cSHORTCUTTxe2x80x9d (trademark) manufactured by T. D. Williamson, Inc., which provides a tap for cutting a coupon out of the pipe wall. Once the pipe has been tapped gas flows through the newly installed bypass pipe, and a stopper is lowered through the fitting and rotated into position to stop gas from flowing into the section of pipe to be bypassed (referred to herein as the xe2x80x9cbypassed pipe sectionxe2x80x9d). This allows the maintenance crew to work on the pipeline under live conditions, and avoids disruption of the gas service to downstream customers.
Once each end of the bypassed pipe section has been stopped, a venting system is installed adjacent to the tee fitting in the bypassed pipe section. For example, venting nipples are welded to the pipe and tested for pressure, then the pipe is tapped through the venting nipples, and venting valves are coupled to the venting nipples. The gas remaining in the bypassed pipe section is blown out through a conduit coupled to the venting system. The bypassed pipe section is then cut off, leaving a short pipe stub, as shown in FIG. 1. The seal provided by the tee fitting stopper is a temporary seal, and in order to complete the operation caps must be welded to the cut ends of the pipe stubs, which remain attached to the tee fitting.
However, the pressure in a live gas pipe can range from low to extra high, and on many occasions the tee fitting stoppers end up resting on cutting debris or an internal pipe seam, and do not provide a complete seal and gas leaks past the stoppers. Although this does not pose a safety hazard, because the gas leakage rate is generally fairly low, the leakage rate can be significant enough that it would be difficult to weld a permanent cap onto the cut ends of the pipe stubs. This is usually determined by the rate of gas flow out of the venting nipples after the bypassed pipe section has been blown out. The welder must judge, based on the rate at which gas is escaping from the venting nipples, whether the conditions are suitable for welding the permanent sealing caps. If the leakage through the tee fitting stopper is low enough, the welder may direct that the bypassed pipe section be cut off, inject an inert gas such as nitrogen into the pipe stub to expel as much natural gas and air as possible from the pipe stub, and then weld the cap. However, if too much gas is leaking through the tee fitting stoppers to weld the cap, the tee fitting stoppers must be reinstalled.
In these cases, the bypassed pipe section cannot be cut off, the system must be re-energized to equalize the pressure on both sides of the tee fitting stoppers so that the stoppers can be dislodged from the pipe and removed. New stoppers must be installed, and the bypassed pipe section blown out again. This adds significant costs to the operation, both direct and indirect. It is a time consuming and laborious process to re-energize the system, replace the stoppers and de-energize the system again. There are cost inefficiencies in the cost of lost gas from repeating the stopping procedure, sometimes multiple times, as well as the cost of the stoppers themselves (which according to the manufacturer""s specifications cannot be reused once they have been removed), which can be in the order of hundreds of dollars per unit, depending upon the size of the pipe. There is also the cost of responding to and investigating notifications of a detected gas leak by neighbouring residents or occupants, who may detect the gas discharged into the air. In addition this poses an environmental hazard, because of the unnecessary release of natural gas into the surrounding environment.
The present invention overcomes these disadvantages by providing a method of sealing a pipe and a device for sealing the pipe which prevents any gas leakage out of the pipe stub remaining attached to the tee fitting of a bypassed pipe section, thus allowing a permanent cap to be welded onto the pipe without the use of nitrogen, and with no difficulties encountered by the welder due to the presence of gas. The method and device of the invention can virtually completely eliminate the failure rate of the temporary seals provided by conventional tee fitting stoppers, so the de-energizing procedure needs to be performed only once, thus avoiding the costs and hazards often associated with ineffective sealing by the tee fitting stoppers.
The invention accomplishes this by providing an expandable plug which provides a completely gas-free environment for welding the permanent cap, by preventing gas leaking through the tee fitting stopper from reaching the cut end of the pipe stub. In the preferred embodiment the plug comprises a pair of plates dimensioned to slide into the pipe, with a sealing member disposed between the plates. The plates are affixed together in a manner which allows them to be squeezed together, for example by tightening nuts onto bolts extending through the plates, such that compression of the sealing member by the plates causes the periphery of the sealing member to expand against the inner wall of the pipe. Stabilizing means, for example a nut having a reverse thread and a complimentary tool for engaging the stabilizing nut, is provided for orienting and stabilizing the expandable plug radially within the pipe as the plates are squeezed together.
The sealing member thus seals the pipe stub between the tee fitting and the cut end of the pipe stub, so that any gas leaking through the tee fitting stopper does not reach the cut end of the pipe stub and is vented out of the venting system. This allows the permanent cap to be effectively and efficiently welded onto the pipe stub to form a permanent seal.
According to the method of the invention, the expandable plug is inserted into the pipe stub after the bypassed pipe section has been removed, and lodged in the pipe stub by squeezing the plates together to expand the sealing member against the inner wall of the pipe stub. A hole is drilled between the expandable plug and the cut end of the pipe stub, so that as the cap is welded onto the pipe stub expanding air within the pipe stub can escape out of the vent hole until the cap weld is complete. The venting system and vent hole are sealed, the tee fitting stopper is removed, and the expandable plug remains in the pipe stub.
The method and device of the invention can save considerable costs and labour. The need to use nitrogen to displace gas leaking into the pipe stub is eliminated, and the permanent cap can be welded to the pipe stub without the need to repeat the stopping process because of leaking tee fitting stoppers.
The present invention thus provides an expandable plug for sealing a pipe, comprising a pair of plates configured for insertion into the pipe, a sealing member disposed between the plates, means for squeezing the plates together to compress the sealing member, and stabilizing means for stabilizing the plug within the pipe as the plates are squeezed together, whereby as the plates are squeezed together the sealing member expands in a radial direction such that a periphery of the sealing member engages an interior wall of the pipe.
The present invention further provides a method of sealing a pipe, comprising the steps of: a. coupling a fitting to the pipe; b. cutting a coupon out of the pipe at the fitting; c. engaging a stopper through the fitting into a position lodged in the pipe; d. cutting the pipe leaving a pipe stub coupled to the fitting; e. inserting into the pipe stub an expandable plug comprising a pair of plates configured for insertion into the pipe, a sealing member disposed between the plates, means for squeezing the plates together to compress the sealing member, and stabilizing means for stabilizing the plug within the pipe as the plates are squeezed together, whereby as the plates are squeezed together the sealing member expands in a radial direction such that a periphery of the sealing member engages an interior wall of the pipe; f. providing a vent hole for the venting of heated air from a portion of the pipe stub between the expandable plug and an open end of the pipe stub, and g. welding a permanent cap over an open end of the pipe stub.
The present invention further provides a method of bypassing a pipe section, comprising the steps of: a. coupling a tee fitting to each end of the pipe section; b. coupling a bypass pipe to each tee fitting; c. cutting a coupon out of the pipe section at each tee fitting; d. engaging a stopper through the tee fitting into a position lodged in the pipe section; e. cutting the pipe section leaving a pipe stub coupled to each tee fitting; f. inserting into each pipe stub an expandable plug comprising a pair of plates configured for insertion into the pipe, a sealing member disposed between the plates, means for squeezing the plates together to compress the sealing member, and stabilizing means for stabilizing the plug within the pipe as the plates are squeezed together, whereby as the plates are squeezed together the sealing member expands in a radial direction such that a periphery of the sealing member engages an interior wall of the pipe; g. providing a vent hole for the venting of heated air from a portion of the pipe stub between the expandable plug and an open end of the pipe stub, and h. welding a permanent cap over an open end of each pipe stub.